Curable hot melt adhesive for casemaking

ABSTRACT

A curable casemaking adhesive, books and related articles bound thereby. In one embodiment, a UV curable hot melt adhesive is used to form the case, which is preferably also embossed. In another embodiment, a moisture curable hot melt adhesive is used to form the case, which is preferably also embossed.

FIELD OF THE INVENTION

[0001] The invention relates to the field of casemaking. Morespecifically, the invention relates to the use of a curable hot meltadhesive and to products, in particular embossed products, constructedwith the use of such an adhesive.

BACKGROUND OF THE INVENTION

[0002] In recent years, substantial interest has grown in thebookbinding, publishing and printing industries, and in the graphic artsarea generally with respect to the development of improved adhesivecompositions which lend themselves to casing-in and casemaking.

[0003] Casing-in is typically accomplished using a water based emulsion.During the casing-in process, a book block is laminated to the inside ofthe cover of a hard bound book by coating the outside of the end sheetsof the book block with the adhesive, and then bonding the cover to theend sheets.

[0004] Casemaking refers to the production of the case or cover, i.e.,the outer shell, of a hard bound book. During this process, the materialthat forms the outer covering of the book is bonded to binder boards toform a “hard” cover. Typically, the covering material is passed along aconveyor during which time binder boards are mated onto the adhesivecoated covering material. The surplus covering material is folded overon to the binder board in a two step process known as “turning in” inwhich either the sides are folded in first and the ends are folded insecond resulting in an overlap of the ends over the sides, or the endsare folded in first and the sides second. These are also called“turn-ins.” Animal glues are typically used for this process, althoughwater based emulsions may also be used.

[0005] Conventional water-based casemaking glues and casing-in pastescontain substantial amounts of water, and moisture from these waterbased systems can be detrimental to a finished book. Moisture from theadhesive can migrate into the binding board or book block causingcockeling or waviness in the end sheets and/or resulting in warpage ofthe cover. The presence of moisture may also result in curvature of thecover in relation to the book block, as can lack of register of thecover with the book block.

[0006] Both hot melt adhesives and reactive hot melt polyurethaneadhesives, also referred to as hot melt moisture curing adhesives, whichcontain no water, have been proposed for use in the bookbindingindustry. Use of a hot melt adhesive for casemaking and/or casing-in isdescribed as reducing warpage during the production of the book and asbestowing a degree of resistance to warp during the life of the book.

[0007] One problem which has not been addressed by prior art hot meltapplications in the casemaking art is the bleed-through which occurswhen the case or cover is embossed, and which damages the embossedsurface. Whereas cases manufactured using animal glues may be embossed,embossing a case manufactured with the use of a hot melt adhesive isdifficult since the adhesive, in contrast to animal glue, tends to flowduring the embossing process. This results in letters, figures, designs,etc. which are not clearly identifiable. The current invention addressesthis need in the art.

SUMMARY OF THE INVENTION

[0008] The invention provides an adhesive for use in casemaking whichminimizes warpage of cases, allows equipment to run in a fast andefficient manner, and allows the case to be embossed without damage tothe embossed surface.

[0009] One aspect of the invention is directed to an adhesive suitablefor use in casemaking and embossing operations.

[0010] Another aspect of the invention is directed to a case or coverfor a hard bound book comprising a curable hot melt adhesive. In oneembodiment, the curable adhesive is a radiation curable adhesive. Apreferred radiation curable adhesive is a UV curable adhesive. In aparticularly useful embodiment, the adhesive is a semi-pressuresensitive UV curable hot melt adhesive based on either high vinylcontent styrene-butidiene-styrene or a mono expoxidized monohydroxylateddiene polymer combined with a tackifier and a napthenic or paraffinicoil, plus initiator and stabilizer. In another embodiment the hot meltadhesive is a moisture curable hot melt adhesive. A preferred moisturecurable hot melt adhesive is based on a blend of urethane and acrylicmonomers or a copolymer of urethane and acrylic monomers.

[0011] Yet another aspect of the invention is directed to an embossedproduct, including but not limited to cases or covers for hard coverbooks.

[0012] Still another aspect of the invention is directed to a method offorming a case or cover by bonding cover boards to book cover stockusing a curable hot melt adhesive.

[0013] One other aspect of the invention is directed to a methodembossing a product, e.g., a case for a hard cover book. An embossedcase is formed by bonding the cover boards to the book cover stock usinga cured hot melt adhesive, and thereafter embossing the case or cover toform an embossed case for a hard cover book.

[0014] A casemaking machine comprising a curing apparatus is alsoencompassed by the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The disclosures of all references cited herein are incorporatedin their entireties by reference.

[0016] The invention is directed to an adhesive suitable for use incasemaking and embossing operations. Casemaking is a series of carefullysynchronized procedures for making the cover of a hard bound book. Ingeneral, the material that will form the outer covering of the book,which is in precut or in continuous web form depending on the type ofapplication equipment used, is coated with adhesive, passed along aconveyer under boards which have been precut to the exact size of thefinished book cover, the boards are dropped in place and a center stripis laid down between the boards. If the cloth was not precut, it is thencut and, in either case, a portion of the cloth extends about ⅝ incharound the perimeter of the cover boards. This extension is then foldedover the boards in a two step “turning-in” process with the sides foldedfirst and the end folded to lap over the sides.

[0017] The adhesive used to construct the book cover or book case mustpossess certain critical properties. Because the operation is amulti-step one, the adhesive chosen must have a relatively long periodof aggressive tack so as to retain sufficient tack to instantly holddown the folded extensions without allowing them to spring back duringthe turning-in step. In addition to its aggressive tack, the adhesiveselected must have good machining properties, and it should be able toadhere a wide variety of case stock materials. Furthermore, once thecase is formed, the adhesive must not penetrate the stock which wouldruin the cover nor may it be affected by moisture, which could causewarping of the cover. Moreover, the cover should be capable of beingembossed, without conventional problems associated with embossingoperations, in particular bleed through.

[0018] Curable hot melt adhesives which may be used in the practice ofthe invention include radiation curable hot melt adhesives and reactive(i.e., moisture curable) hot melt adhesives. A hot melt adhesive is athermoplastic material, solid at room temperature, which is applied inits molten form and will adhere to a surface when cooled to atemperature below its melting point. Hot melt adhesives differ fromother liquid adhesives in that they set simply by cooling rather than bychemical curing or the evaporation of a solvent. In a curable hot meltadhesive, crosslinking occurs by a variety of mechanisms depending onthe formulation, such as by exposure to UV irradiation or by exposure tomoisture. In radiation curable hot melt adhesives, crosslinking occursupon exposure to actinic and/or ionizing radiation. Reactive hot meltpolyurethane adhesives depend on the presence of moisture, which isobtained from the substrates or atmosphere, to cure which involvescrosslinking to form tough, resilient adhesives.

[0019] The curable hot melt adhesives used in the practice of theinvention may, desirably, be pressure sensitive or semi-pressuresensitive. As used herein, the term “pressure-sensitive adhesive” refersto a viscoelastic material which adheres instantaneously to mostsubstrates with the application of slight pressure and remainspermanently tacky. A polymer is a pressure-sensitive adhesive within themeaning of the term as used herein if it has the properties of apressure-sensitive adhesive per se or functions as a pressure-sensitiveadhesive by admixture with tackifiers, plasticizers or other additives.A semi-pressure sensitive adhesive is one which temporarily possessessufficient tack to permanently bond the substrate. After this time theadhesive is still permanently tacky but not enough to create a strongbond. Semi-pressure sensitive adhesives are typically used as regularhot melts. That is the bond is made while the adhesive is still molten.The fact that bondable tack extends through the solidification stagecreates the opportunity to bond over a wide process range. One cannotcoat these types of adhesive and create a bond with them at a later dateas with a true pressure sensitive.

[0020] The term “curable” is used herein in its conventional sense asmeaning capable of forming covalent cross-links.

[0021] The term “radiation-curable adhesive” as used herein means anadhesive composition which is curable upon exposure to actinic and/orionizing radiation. The term “radiation” is used herein to includeactinic radiation such as ultraviolet radiation and ionizing radiationcreated by the emission of electrons or highly accelerated nuclearparticles such as neutrons, alpha-particles etc.

[0022] The adhesive is used in casemaking operations to bond the coverboards to the cover stock. The cover board or binder boards aregenerally chip board that has been compressed to give a high burstingstrength board, sometimes designated chestnut cover board. Cover stockmaterials useful for making book covers include, for example, cloth,paper, leather, vinyl, polyethylene, composite materials such as paperor cloth laminated to polyethylene, polyester, or “mylar,” andpolypropylene, woven fabric, pryoxylin, vinyl or other resin impregnatedor coated fabric. In addition a synthetic material comprising aspunbonded olefin of high density polyethylene fibers available from E.I. DuPont de Nemours and Co., Inc. under the tradename Tyvec may be usedBuckram, a conventional library stock material, may also be used in thepractice of the invention. The curable hot melt adhesives used hereinallow production of cases without limitation to the type of cover stockor cloth used. Use of a curable hot melt adhesive in the preparation ofan embossed case or cover in accordance with the invention isparticularly useful when employing a porous cover stock.

[0023] Previous synthetic adhesive approaches have either lacked theability to emboss without bleed through or lacked the cohesion whenfreshly applied thus producing debonding at the corners of the casewhere the facing substrate is folded over. It has now been discoveredthat use of curable hot melt adhesives in accordance with the inventionwill enable the casemaker to emboss the case or cover without damage tothe embossed surface of the type heretofore encountered in the art. Thisis accomplished by the cure, which renders the adhesive non-flowing.

[0024] In accordance with the practice of the invention, a case or coverfor a hard bound book is typically formed by applying a curable hot meltadhesive to the cover stock, exposing the adhesive to curing conditions(e.g., UV, IR, electron beam, moisture) and bonding the book cover stockto the cover boards. As will be appreciated, depending on the adhesiveused, the cover stock may be bonded to the cover board before beingsubjected to curing conditions. While the adhesive is preferably appliedto the cover stock, application of adhesive to the cover board is alsopossible.

[0025] The cover may be embossed, as conventional in the art, usingcommercially available embossing machine. While separate embossingmachinery is typically used for embossing the finished case, thecasemaking machinery may comprises an embossing apparatus or mechanism.While embossing typically will be accomplished on the finished caseprior to casing-in, embossing may also be accomplished on the finishedbook, e.g., for the purpose of monogramming, dedication, personalizationor the like.

[0026] While the disclosure describes in detail preparation of anembossed case or cover, other embossed products are encompassed by theinvention. Such embossed products include but are not limited to gift orpackaging boxes and the like, jewelry boxes, suitcases, briefcases, andautomobile interiors. The products are manufacture by bonding a backingsubstrate to a cover substrate using a curable hot melt adhesive, andthereafter embossing the cover side of the laminated substrate.

[0027] Any conventional casemaking machine modified to accommodate a hotmelt adhesive may be used in the practice of the invention, such asthose available from Kolbus and from Crathern. Various modificationshave been described in the art. See, e.g., Mielke, G. B., November 1974,Book Production Industry 50(6):31-32, 34.

[0028] In general, a cover material such as a sheet of cloth or sheet ofpaper is feed through a spreader/gluer where a uniform coating of moltenradiation curable or moisture curable hot melt adhesive is applied tothe material. The adhesive may be applied by a variety of methodsincluding coating or spraying in an amount sufficient to cause the covermaterial to adhere to the cover board. The freshly glued cover materialis typically passed through a curing apparatus and then bonded to binderboards. The glued cover material/board proceeds to a turning in stationwhere all four sides of the cover material are turned in, or wrappedaround the edges of the cover boards. Some machines may also comprise amitering station which cuts away the cover material at a 45° angle toallow a neat tuck and a well formed corner. The cover is then fedthrough a rotary press where the cover is pressed to insure that thecover material and boards are securely laminated.

[0029] Preferred radiation curable adhesives comprise at least one highvinyl block copolymer. High vinyl block styrene-butadiene-styrenecopolymers and/or styrene-isoprene-styrene copolymers are preferred.While radial and linear block copolymers are preferred for use, otherblock copolymer morphologies can be used as would be recognized by thoseskilled in the art. The term bock copolymers include di-block, tri-blockand mult-block copolymers.

[0030] Examples of radiation curable hot melt adhesives which may beused in the practice of the invention will typically comprise from about5% to about 40% by weight of at least one high vinyl blockstyrene-butadiene copolymer; from about 30% to about 80% by weight of atleast one solid tackifier; from about 0.05% to about 5% by weight of atleast one photoinitiator; up to about 15% by weight of at least one highvinyl, linear styrene-butadiene-styrene or multi-block styrene-butadienecopolymer; up to about 15% by weight of at least one high diblockconventional low vinyl styrene-butadiene-styrene orstyrene-isoprene-styrene block copolymer; up to about about 40% byweight of at least one oil or liquid tackifier; and up to about 3% byweight of at least one antioxidant.

[0031] Suitable high vinyl styrene-butadiene block copolymers include,but are not limited to, four arm radial multi-block styrene-butadienecopolymers comprising 60% vinyl, 26% styrene and a relatively broadmolecular weight distribution (Mn=94,200 and Mw=276,100). Such blockcopolymers include SR8296 available from Firestone.

[0032] Suitable high vinyl linear styrene-butadiene block copolymersinclude, but are not limited to, linear multi-block styrene-butadienecopolymers having 57% vinyl, 44% styrene, melt index=13 (cond. G),(Mw=85,000 and Mn=54,000). Such copolymers include STEREON 857 availablefrom Firestone.

[0033] Suitable high diblock conventional low vinylstyrene-butadiene-styrene, or SIS, block copolymers include AsapreneJT38; Kraton D1119; Quintac SL117; SR 8219.

[0034] Multi-block copolymers may be prepared by a variety of methods.One such method is described in U.S. Pat. No. 3,937,760 (The FirestoneTire & Rubber Company). A typical multi-block copolymer is SR8296. Thisis a four arm radial multi-block styrene-butadiene copolymer comprising60% vinyl, 26% styrene and a relatively broad molecular weightdistribution (Mn=94,200 and Mw=276,100) and is available from Firestone.

[0035] Solid hydrogenated tackifying resins are useful in the radiationcurable composition of the invention in concentrations ranging fromabout 30% by weight to about 80% by weight, preferably in amountsranging from about 45% by weight to about 70%, more preferably fromabout 50% by weight to about 65% by weight.

[0036] Representative tackifying resins include the C₅/C₉ hydrocarbonresins, synthetic polyterpenes, rosin, rosin esters, natural terpenes,and the like. More particularly, the useful tackifying resins includeany compatible resins or mixtures thereof such as (1) natural andmodified rosins including gum rosin, wood rosin, tall oil rosin,distilled rosin, hydrogenated rosin, dimerized rosin, and polymerizedrosin; (2) glycerol and pentaerythritol esters of natural and modifiedrosins, including the glycerol ester of pale, wood rosin, the glycerolester of hydrogenated rosin, the glycerol ester of polymerized rosin,the pentaerythritol ester of hydrogenated rosin, and thephenolic-modified pentaerythritol ester of rosin; (3) copolymers andterpolymers of natural terpenes, such as styrene/terpene and alphamethyl styrene/terpene; (4) polyterpene resins generally resulting fromthe polymerization of terpene hydrocarbons, such as the bicyclicmonoterpene known as pinene, in the presence of Friedel-Crafts catalystsat moderately low temperatures; also included are the hydrogenatedpolyterpene resins; (5) phenolic modified terpene resins andhydrogenated derivatives thereof such, for example, as the resin productresulting from the condensation, in an acidic medium, of a bicyclicterpene and a phenol; (6) aliphatic petroleum hydrocarbon resinsresulting from the polymerization of monomers consisting primarily ofolefins and diolefins; also included are the hydrogenated aliphaticpetroleum hydrocarbon resins; and (7) cyclic petroleum hydrocarbonresins and the hydrogenated derivatives thereof. Also included are thecyclic or acyclic C₅ resins and aromatic modified acyclic or cyclicresins. Preferred are hydrogenated, cyclic or C₅ resins, such as Escorez5400 (Exxon), hydrogenated aromatic modified cyclic resin ECR179EX(Exxon). Mixtures of two or more of the above described tackifyingresins may be required for some formulations.

[0037] The photoinitiators are typically employed in concentrationsranging from about 0.05% by weight to about 5% by weight, preferably inamounts ranging from about 0.2% by weight to about 3% by weight, morepreferably from about 0.5% by weight to about 1.5% by weight. Theconcentration is chosen based on the thickness of the application of theuncured radiation curable composition. Combinations of two or morephotinitiators may also be used. Commercial examples include Irgacure651, 184 and 1700 and Darocur 1173, available from Ciba-Geigy as well asGenocure LBP available from Rahn, and Esacure KIP150 available fromSartomer. Other examples of photoinitiators include benzophenone,benzyidimethyl ketal, isopropylthioxanthone,bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl) phosphineoxide,2-hydroxy-2-methyl-1-phenyl-1-propanone,diphenyl(2,4,6-trimethybenzoyl)phosphine oxides, 1-hydroxycyclohexylphenyl ketone,2-benzyl-2-(dimethylamino)-1-)4-(4-morpholinyl)phenyl-1-butanone,alpha,alpha-dimethoxy-alpha-phenylacetophenone,2,2-diethoxyacetophenone,2-methyl-1-)4-(methylthio)phenyl-2-(4-morpholinyl)-1- -propanone, and2-hydroxy-1-4-(hydroxyethoxy)phenyl-2-methyl-1-propanone.

[0038] Combinations of photoinitiators may be used to achieve the bestpossible cure of adhesive compositions. Photoinitiators are preferablyused in the least amount necessary to get initiation of cure at the linespeed of the process. The cure process is generally more efficient inthe absence of oxygen, for example, in the presence of nitrogen, so agreater amount of photoinitiator is generally required in the presenceof oxygen.

[0039] The hot melt adhesive of the present invention may also compriseabout 0% by weight to about 40% by weight of an oil diluent. Suitableplasticizing or extending oils include olefin oligomers and lowmolecular weight polymers as well as vegetable and animal oil and theirderivatives. The petroleum derived oils which may be employed arerelatively high boiling materials containing only a minor proportion ofaromatic hydrocarbons (preferably less than 30% and, more particularly,less than 15% by weight of the oil). Alternatively, the oil may betotally non-aromatic. Suitable oligomers include polypropylenes,polybutenes, hydrogenated polyisoprene, hydrogenated polybutadiene, orthe like having average molecular weights between about 350 and about10,000. Preferred are LUMINOL T350, a mineral oil available fromPetrocanada and KAYDOL OIL available from Witco Corporation.

[0040] Antioxidants are typically added to the commercially availablecompounds in order to protect the ingredients against degradation duringpreparation and use of the adhesive compositions, however withoutinterfering with the irradiation curing of the polymer. Combinations ofantioxidants are often more effective due to the different mechanisms ofdegradation to which various polymers are subject. Certain hinderedphenols, organo-metallic compounds, aromatic amines, aromaticphosphites, and sulphur compounds are useful for this purpose. Examplesof effective types of these materials include phenolic antioxidants,thio compounds, and tris-(nonylated phenyl) phosphites.

[0041] Examples of commercially available antioxidants include IRGANOX1010 (pentaetythrityl-tetrakis[3-(3,5-di-tert--butyl-4-hydroxyphenyl)propionate); IONOL(2,6-di-tertiary-butyl-4-methyl phenol); IONOX 330 (3,4,6-tris(3,5-di-tertiary-butyl-p-hydroxybenzyl)-1,3,5-trimethylbenzene); andPOLYGARD HR (tris-(2,4-di-tertiary-butyl-phenyl) phosphite).

[0042] To ensure long-term thermal stability, in general from about 0.1%to about 3% by weight of one or more antioxidants is included in theadhesive compositions, preferably from about 0.4% by weight to about1.5% by weight.

[0043] Additional materials may be added optionally to the adhesivecomposition at up to about 15% by weight, preferably from about 5% byweight to about 10% by weight, dependent on the intended end-use of theadhesive. Such additional materials include, without limitation, blockcopolymers of monovinyl aromatic hydrocarbons and conjugated dienes suchas polystyrene-polybutadiene-polystyrene,polystyrene-polyisoprene-polystyrene,poly(alpha-methyl-styrene)-polybutadiene-poly(alpha-methyl-styrene),poly(alpha-methyl-styrene)-polyisoprene-poly(alpha-methyl-styrene), aswell as the hydrogenated modifications thereof, e.g.polystyrene-poly(ethylene-butylene)-polystyrene andpolystyrene-poly(ethylene-propylene)-polystyrene. These copolymers maybe prepared by methods taught, for example, in U.S. Pat. Nos. 3,239,478;3,247,269; 3,700,633; 3,753,936; and 3,932,327, and are available fromseveral manufacturers, including Shell Chemical Co. under the trade nameKRATON.

[0044] Other non-limiting examples of additional materials include SBRrandom copolymers with low (<20%) or high (>20%) vinyl contents,available under the tradename DURADENE from Firestone (these high vinylcopolymers are reactive and contribute to the crosslinking of thesystem); EPDM copolymers which can react into the polymer network viaunsaturated sites, and saturated analogs (e.g. EP rubber) that canmodify the peel and tack of the adhesive and which are available fromExxon under the trade name VISTALON; butyl rubber, which is a copolymerof isoprene and isobutylene and is available from Exxon Chemical Companyunder the trade name SB BUTYL; Polyisobutylene, available from ExxonChemical Company under the trade name VISTANEX; and liquidpolyisopropylene such as is available from Kuraray Inc. under the tradename LIR.

[0045] In addition to the above-described additional materials, thevarious compositions of the present invention may include otheradditives known to those skilled in the art. These additives mayinclude, but are not limited to, pigments, fillers, fluorescentadditives, flow and leveling additives, wetting agents, surfactants,antifoaming agents, rheology modifiers, stabilizers, and antioxidants.Preferred additives are those which do not have appreciable absorptionin the wavelengths of interest.

[0046] Examples of pigments and filler materials include, but are notlimited to, titanium dioxide, hydrophobic amorphous fumed silica,amorphous precipitated silica, carbon black, and polymer powders.Examples of flow and leveling additives, wetting agents, and antifoamingagents include silicones, hydrocarbons, fluorine-containing compounds,and non-silicone polymers and copolymers such as copolyacrylates.

[0047] Other materials which may be added optionally to the adhesivecomposition include endblock resins which are substantially aromatic.Examples of such endblock resins can be prepared from any substantiallyaromatic monomers having a polymerizable unsaturated group. Typicalexamples of such aromatic monomers include the styrenic monomers,styrene, alpha-methyl styrene, vinyl toluene, methoxy styrene, tertiarybutyl styrene, chloro styrene, etc., indene monomers including indene,and methyl indene. The aromatic endblock resin is preferably present inamounts of 5 to 20 weight percent. Preferred is HERCOLITE 240 orKRISTALEX 5140, both of which are alpha methyl styrene resins availablefrom Hercules, Inc.

[0048] In a preferred embodiment of the present invention the adhesivecomposition comprises from about 20% to about 30% by weight blockstyrene-butadiene copolymer having about 60% by weight vinyl and about26% by weight styrene; from about 45% to about 60% by weight of ahydrogenated tackifier resin; from about 0.5% to about 1.5% by weight ofa photoinitiator; from about 10% to about 20% by weight of a whitemineral oil; from about 0% to about 0.5% by weight of an acrylicantioxidant, from about 0% to about 0.5% by weight of a thioesterantioxidant, and from about about 0% to about 0.5% by weight of ahindered phenol antioxidant; and from about 0% to about 10% by weight ofa diblock copolymer.

[0049] For purpose of illustration, an adhesive composition useful inthe practice of the invention comprises about 24% by weight blockstyrene-butadiene copolymer having about 60% by weight vinyl and about26% by weight styrene; about 49.5% by weight of a DCPD tackifier resin;about 0.8% by weight of a photoinitiator; about 18% by weight of a whitemineral oil; about 0.3% by weight of an acrylic antioxidant; about 0.3%by weight of a thioester antioxidant; about 0.2% by weight of a hinderedphenol antioxidant; and about 6% by weight of an SB diblock copolymer.

[0050] The adhesive compositions of the invention are prepared byconventional methods. As an example, the block copolymers, thetackifying resin and other desired components may be blended at anelevated temperature, (e.g. temperature of about 300° F.) using anextruder, a Z-blade mixer or other conventional mixing device. Apreferred method employs the process as disclosed in U.S. Pat. No.3,937,760, the disclosure of which is incorporated herein by reference.

[0051] Polyurethane hot melt adhesives are comprised ofisocyanate-terminated polyurethane polymers, often referred to as“prepolymers,” that react with surface or ambient moisture in order tochain-extend and form a second polyurethane polymer.

[0052] Unlike conventional hot melt adhesives, which can be heated to aliquid state and cooled to a solid state repeatedly, a reactive hot meltundergoes an irreversible chemical reaction to a solid “cured” form oncedispensed in the presence of ambient moisture.

[0053] The urethane prepolymers are those conventionally used in theproduction of polyurethane hot melt adhesive compositions. Any suitablecompound which contains two or more isocyanate groups may be used forpreparing the urethane prepolymers. Typically from about 5 to about 75parts by weight of an isocyanate is used.

[0054] Organic polyisocyanate which may be used to practice theinvention include alkylene diisocyanates, cycloalkylene diisocyanates,aromatic diisocyanates and aliphatic-aromatic diisocyanates. Specificexamples of suitable isocyanate-containing compounds include, but arenot limited to, ethylene diisocyanate, ethylidene diisocyanate,propylene diisocyanate, butylene diisocyanate, trimethylenediisocyanate, hexamethylene diisocyanate, toluene diisocyanate,cyclopentylene-1,3-diisocyanate, cyclo-hexylene-1,4-diisocyanate,cyclohexylene-1,2-diisocyanate, 4,4′-diphenylmethane diisocyanate,2,2-diphenylpropane-4,4′-diisocyanate, xylylene diisocyanate,1,4-naphthylene diisocyanate, 1,5-naphthylene diisocyanate, m-phenylenediisocyanate, p-phenylene diisocyanate, diphenyl-4,4′-diisocyanate,azobenzene-4,4′-diisocyanate, diphenylsulphone-4,4′-diisocyanate,2,4-tolylene diisocyanate, dichlorohexa-methylene diisocyanate,furfurylidene diisocyanate, 1-chlorobenzene-2,4-diisocyanate,4,4′,4″-triisocyanatotriphenylmethane, 1,3,5-triisocyanatobenzene,2,4,6-triisocyanato-toluene,4,4′-dimethyldiphenyl-methane-2,2′,5,5-tetratetraisocyanate, and thelike. While such compounds are commercially available, methods forsynthesizing such compounds are well-known in the art. Preferredisocyanate-containing compounds are methylenebisphenyidiisocyanate(MDI), isophoronediisocyanate (IPDI) and toluene diisocyanate (TDI).

[0055] Most commonly, the prepolymer is prepared by the condensationpolymerization of a polyisocyanate with a polyol, most preferably thepolymerization of a diisocyanate with a diol. The polyols used includepolyhydroxy ethers (substituted or unsubstituted polyalkylene etherglycols or polyhydroxy polyalkylene ethers), polyhydroxy polyesters, theethylene or propylene oxide adducts of polyols and the monosubstitutedesters of glycerol, as well as mixtures thereof. The polyol is typicallyused in an amount of between about 1 to about 70 parts by weight.

[0056] Examples of polyether polyols include a linear and/or branchedpolyether having plural numbers of ether bondings and at least twohydroxyl groups, and contain substantially no functional group otherthan the hydroxyl groups. Examples of the polyether polyol may includepolyoxyalkylene polyol such as polyethylene glycol, polypropyleneglycol, polybutylene glycol and the like. Further, a homopolymer and acopolymer of the polyoxyalkylene polyols may also be employed.Particularly preferable copolymers of the polyoxyalkylene polyols mayinclude an adduct at least one compound selected from the groupconsisting of ethylene glycol, propylene glycol, diethylene glycol,dipropylene glycol, triethylene glycol, 2-ethylhexanediol-1,3, glycerin,1,2,6-hexane triol, trimethylol propane, trimethylol ethane,tris(hydroxyphenyl)propane, triethanolamine, triisopropanolamine,ethylenediamine and ethanolamine; with at least one compound selectedfrom the group consisting of ethylene oxide, propylene oxide andbutylene oxide.

[0057] A number of suitable polyols available commercially. By way ofexample only, there is mentioned CP4701 (Dow Chemicals), Niax 11-34(Union Carbide Corp), Desmophen 3900 (Bayer), Propylan M12 (LankroChemicals), Highflex 303 (Daiichi Kogyo Seiyaku K.K.) and Daltocel T32-75 (ICI). “Polymer polyols” are also suitable, i.e. graft polyolscontaining a proportion of a vinyl monomer, polymerised in situ, e.g.,Niax 34-28.

[0058] Polyester polyols are formed from the condensation of one or morepolyhydric alcohols having from 2 to 15 carbon atoms with one or morepolycarboxylic acids having from 2 to 14 carbon atoms. Examples ofsuitable polyhydric alcohols include ethylene glycol, propylene glycolsuch as 1,2-propylene glycol and 1,3-propylene glycol, glycerol,pentaerythritol, trimethylolpropane, 1,4,6-octanetriol, butanediol,pentanediol, hexanediol, dodecanediol, octanediol, chloropentanediol,glycerol monallyl ether, glycerol monoethyl ether, diethylene glycol,2-ethylhexanediol-1,4, cyclohexanediol-1,4, 1,2,6-hexanetriol,1,3,5-hexanetriol, 1,3-bis-(2-hydroxyethoxy)propane and the like.Examples of polycarboxylic acids include phthalic acid, isophthalicacid, terephthalic acid, tetrachlorophthalic acid, maleic acid,dodecylmaleic acid, octadecenylmaleic acid, fumaric acid, aconitic acid,trimellitic acid, tricarballylic acid, 3,3′-thiodipropionic acid,succinic acid, adipic acid, malonic acid, glutaric acid, pimelic acid,sebacic acid, cyclohexane-1,2-dicarboxylic acid,1,4-cyclohexadiene-1,2-dicarboxylic acid,3-methyl-3,5-cyclohexadiene-1,2-dicarboxylic acid and the correspondingacid anhydrides, acid chlorides and acid esters such as phthalicanhydride, phthaloyl chloride and the dimethyl ester of phthalic acid.Preferred polycarboxylic acids are the aliphatic and cycloaliphaticdicarboxylic acids containing no more than 14 carbon atoms and thearomatic dicarboxylic acids containing no more than 14 atoms.

[0059] In addition, the urethane prepolymers may be prepared by thereaction of a polyisocyanate with a polyamino or apolymercapto-containing compound such as diamino polypropylene glycol ordiamino polyethylene glycol or polythioethers such as the condensationproducts of thiodiglycol either alone or in combination with otherglycols such as ethylene glycol, 1,2-propylene glycol or with otherpolyhydroxy compounds disclosed above. In accordance with one embodimentof the invention, the hydroxyl containing acrylic polymer may functionas the polyol component, in which case, no additional polyol need beadded to the reaction.

[0060] Further, small amounts of low molecular weight dihydroxy,diamino, or amino hydroxy compounds may be used such as saturated andunsaturated glycols, e.g., ethylene glycol or condensates thereof suchas diethylene glycol, triethylene glycol, and the like; ethylenediamine, hexamethylene diamine and the like; ethanolamine,propanolamine, N-methyidiethanolamine and the like.

[0061] The reactive hot melt adhesive may also be modified byincorporation of acrylic polymers, as describe in U.S. Patent No.5,021,507 and U.S. Patent No. 5,866,656, and/or by incorporation ofethylene vinyl acetate copolymers.

[0062] In a preferred embodiment of the invention, the urethane ismodified by the incorporation of acrylic resins, in particular reactivehydroxy-containing and non-reactive acrylic copolymers. Preferablybetween about 0 to about 80%, more preferably from about 0 to about 40%,most preferably from about 15 to about 35%, by weight of thehydroxylated and or non-hydroxylated acrylic polymer is present in thein the adhesive composition.

[0063] Virtually any ethylenically unsaturated monomer containinghydroxyl functionality greater than one may be utilized in thecompositions of the present invention. Most commonly employed arehydroxyl substituted C₁ to C₁₂ esters of acrylic and methacrylic acidsincluding, but not limited to hydroxyl substituted methyl acrylate,ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isobutylacrylate, n-propyl or iso-propyl acrylate or the correspondingmethacrylates. Mixtures of compatible (meth)acrylate monomers may alsobe used. Additional monomers that may be used include the hydroxylsubstituted vinyl esters (vinyl acetate and vinyl propionate), vinylethers, fumarates, maleates, styrene, acrylonitrile, etc. as well ascomonomers thereof.

[0064] If used as monomers, these monomers are blended with othercopolymerizable comonomers as formulated so as to have a wide range ofTg values, as between about −48° C. and 105° C., preferably 15° C. to85° C. Suitable comonomers include the C₁ to C₁₂ esters of acrylic andmethacrylic acids including, but not limited to methyl acrylate, ethylacrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate,n-propyl or iso-propyl acrylate or the corresponding methacrylates.Mixtures of compatible (meth)acrylate monomers may also be used.Additional monomers that may be used include the vinyl esters (vinylacetate and vinyl propionate), vinyl ethers, fumarates, maleates,styrene, acrylonitrile, ethylene, etc. as well as comonomers thereof.

[0065] The hydroxyl containing monomers may be the same or differentfrom the monomers used in the remainder of the acrylic polymerization.The particular monomers selected will depend, in large part, upon theend use for which the adhesives are intended. Thus, adhesives to be usedin pressure sensitive applications or in applications wherein adhesionto metal is required will be selected to obtain a lower Tg polymer thanmay be desired in non-pressure sensitive applications or those involvingmore easily bonded substrates.

[0066] When the adhesive is to be prepared utilizing monomericmaterials, the respective monomers may be added to the polyols andpolymerized therein prior to formation of the prepolymer or may be addedto the already formed prepolymer and the acrylic polymerizationsubsequently performed. In the case of polyamino or polymercaptocontaining prepolymers, in-situ vinylic polymerization must be performedonly in the pre-formed prepolymer.

[0067] The hydroxyl containing ethylenically unsaturated monomer ispolymerized using conventional free radical polymerization procedures toa relatively low molecular weight. For purposes of clarification herein,by “low molecular weight” is meant number average molecular weights inthe range of approximately 2,000 to 25,000, preferably 4,000 to 15,000.

[0068] Molecular weight distribution is characterized by Gel PermeationChromatography using a PL Gel Mixed 10 micron column, a Shimadzu ModelRID 6A Detector with a tetrahydrofuran carrier solvent at a flow rate of1 milliliter per minute. The low molecular weight is obtained by carefulmonitoring and controlling the reaction conditions and, generally, bycarrying out the reaction in the presence of a chain transfer agent suchas dodecyl mercaptan. Subsequent to the polymerization of theethylenically unsaturated monomer(s), the polyisocyanate and anyadditional ingredients required for the urethane prepolymer formingreaction are added and that reaction is carried out using conventionalcondensation polymerization procedures. In this manner, the resultantisocyanate terminated urethane prepolymer forms the reactive curing hotmelt adhesive described above which contains about 10 to 70% of theurethane prepolymer and 30 to 90% of the low molecular weight hydroxylcontaining polymer.

[0069] It is also possible to polymerize the low molecular weightpolymer in the presence of the already formed isocyanate terminatedurethane prepolymer. This method has the drawback of subjecting theprepolymer to unnecessary heating during the acrylic polymerization,heating that might result in branching, viscosity increase, depletion ofneeded isocyanate groups and possible gellation. Although thesedisadvantages are subject to control, more stringent control ofconditions are required as compared to polymerization in thenon-isocyanate functional urethane components. When the reaction is runin the polyol or other non-isocyanate containing component, there isalso the advantage of lower reaction viscosities and reduced exposure toisocyanate vapors because of the lesser amount of heating required.

[0070] Optionally, the hydroxyl containing functionality may beintroduced into the adhesive in the form of pre-polymerized lowmolecular weight hydroxyl containing polymers. In the latter case,typical polymers include hydroxyl substituted butyl acrylate,hydroxylated butyl acrylate/methyl methacrylate copolymers, hydroxylatedethyl acrylate/methyl methacrylate copolymers, and the like, thepolymers having a number average molecular weight of 2,000 to 25,000 anda hydroxyl number of 5 to 15. If used in the form of low molecularweight polymers, the polymers may be blended with the polyol prior toreaction thereof with the isocyanate or they may be added directly tothe isocyanate terminated prepolymer.

[0071] Preferred adhesives of the invention typically comprise fromabout 5 to about 50 parts by weight of an isocyante, from about 1 toabout 70 parts by weight of a polyol, and from about 0 to about 80 partsby weight of an acrylic copolymer. The polyol may be a polyester polyol,a polyether polyol or a combination thereof.

[0072] While the adhesives may be used directly as described above, ifdesired the adhesives of the present invention may also be formulatedwith conventional additives which are compatible with the composition.Such additives include plasticizers, compatible tackifiers, catalysts,fillers, anti-oxidants, pigments, adhesion promoters, stabilizers andthe like. Conventional additives which are compatible with a compositionaccording to this invention may simply be determined by combining apotential additive with the composition and determining if they arecompatible. An additive is compatible if it is homogenous within theproduct.

[0073] The reactive hot melt adhesives of the invention may also containflame retardant components. Fire retardant additives known in the artfor imparting flame resistance to polyurethane compositions may beadded. Such compounds include inorganic compounds such as a boroncompound, aluminum hydroxide, antimony trioxide and the like, and otherhalogen compounds including halogen-containing phosphate compounds suchas tris(chloroethyl)phosphate, tris(2,3-dichloropropyl)-phosphate, andthe like. These and other flame retarding compositions are described inU.S. Pat. Nos. 3,773,695 4,266,042, 4,585,806, 4,587,273 and 4,849,467,and European Patent No. 0 587 942. In a preferred embodiment,ethylenebistetrabromophthalimide and/ortris(2,3-dibromopropyl)-isocyanurate is added as a prime flame retardantcomponent. The ethylenebistetrabromophthalimide and/ortris(2,3-dibromopropyl)isocyanurate may be used with or without otherflame retardants. The composition may further comprise a chlorinatedparaffin and/or an aryl phosphate ester as a further flame retardantcomponent. The optional chlorinated paraffin imparts flame retardancy aswell as performing as a viscosity modifier. The aryl phosphate esterfurther imparts improved adhesion to the substrates. The flame retardantpolyurethane-based reactive hot melt adhesives when used in the practiceof the invention gives excellent flame retardancy while maintaining thetargeted properties of the base polymer, such as good green strength,controlled setting speed and good thermal stability at elevatedtemperatures.

[0074] When a reactive hot melt is used in the practice of theinvention, the finished case is subjected to conditions which will allowthe adhesive to cure to a composition having an irreversible solid form,said conditions comprising moisture.

[0075] The invention can be illustrated by the following non-limitingexamples.

EXAMPLE

[0076] Adhesive samples were prepared by melting and mixing untilhomogeneous components listed in Table 1 (% by weight). Mix temperatureswere held at about 350° F. Each adhesive was prepared by firstdissolving any stabilizers in the diluent and then adding polymer. Afterthe polymer was melted and homogenized the tackifying resin was addedand mixed until fully and uniformly dissolved. TABLE 1 A B C D E SR-829622 0 0 0 0 Stereon 857 0 22 24 26 26 Escorez 5400 54.5 54.5 52.6 50.6 0Escorez 5300 0 0 0 0 50.6 Kaydol USP 22 22 22 22 22 Irgacure 651 0.8 0.80.8 0.8 0.8 Irganox 3052 0.3 0.3 0.3 0.3 0.3 Viscosity @ 300° F. 17,3002,700 3140 4300 5087 (cps)

[0077] SR-8296 is a high vinyl four arm radial multi-blockstyrene-butadiene copolymer commercially available from Firestonecomprising 60% vinyl, 26% styrene and a molecular weight distribution orapproximately (Mn=94,200 and Mw=276,100). Stereon 857 is a high vinyllinear styrene-butadiene multi-block copolymer having 57% vinyl, 44%styrene, melt index=13 (cond. G), (Mw=85,000 and Mn=54,000) availablefrom Firestone. Escorez 5400 is a hydrogenated cyclic or C₅ resinavailable from Exxon. Escorez 5300 is a hydrogenated DCPD resinavailable from Exxon. Kaydol USP is a substantially non-aromaticpetroleum based oil available from Witco Corporation. Irgacure 651 is aphoto-initiator available from Ciba Giegy. Irganox 3052 is ananti-oxidant stabilizer available from Ciba Giegy.

[0078] The formulation of Sample A used SR-8296. Rheology comparison ofanimal glue to the adhesive formulation of Sample A cured and uncuredshows that in the cured state adhesive Sample A behaves equivalently tothe animal glue, thus affording freedom from bleed through in theembossing operation.

[0079] The formulation of Samples B, C and D use another high vinylpolymer Stereon 857. Rheology of these products also shows excellentsimilarity to animal glue. These formulations have the added advantageof viscosity equivalence to animal glue thus requiring less modificationof current application equipment. Sample D provided an excellent balanceof viscosity and cured rheology.

[0080] The formulation of Sample E contains an alternate preferredtackifier. Rheology shows it works well in simulating the performance ofanimal glue also.

[0081] Many modifications and variations of this invention can be madewithout departing from its spirit and scope, as will be apparent tothose skilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A case for a hard cover book comprising a curable hot melt adhesive.2. The case of claim 1 wherein the case comprises a radiation curablehot melt adhesive.
 3. The case of claim 2 wherein the radiation curablehot melt adhesive is a UV curable hot melt adhesive.
 4. The case ofclaim 1 wherein the case comprises a moisture curable hot melt adhesive.5. The case of claim 1 wherein the adhesive comprises at least one blockcopolymer comprising a high vinyl styrene-butadiene-styrene blockcopolymer and a photoinitiator.
 6. The case of claim 1 wherein the blockcopolymer is a radial block copolymer.
 7. The case of claim 1 whereinthe block copolymer is a linear block copolymer.
 8. The case of claim 1wherein the adhesive comprises a mono epoxidized mono hydrated dienepolymer and a photoinitiator.
 9. The case of claim 1 which is embossed.10. The case of claim 1 comprising cover boards and a porous coverstock.
 11. An embossed product comprising a cured hot melt adhesive. 12.The product of claim 11 wherein the cured hot melt adhesive is aradiation cured hot melt adhesive.
 13. The product of claim 11 whereinthe cured hot melt adhesive is a moisture cured hot melt adhesive.
 14. Amethod of forming a case for a hard cover book comprising bonding coverboards to cover stock material using a curable hot melt adhesive. 15.The method of claim 14 wherein the curable adhesive is a radiationcurable hot melt adhesive.
 16. The method of claim 15 wherein theradiation curable hot melt adhesive is a UV curable hot melt adhesive.17. The method of claim 14 wherein the curable adhesive comprises amoisture curable hot melt adhesive.
 18. The method of claim 15 whereinthe adhesive comprises at least one block copolymer comprising a highvinyl styrene-butadiene-styrene block copolymer and a photoinitiator.19. The method of claim 18 wherein the block copolymer is a radial blockcopolymer.
 20. The method of claim 18 wherein the block copolymer is alinear block copolymer.
 21. The method of claim 14 wherein the adhesivecomprises a mono epoxidized mono hydrated diene polymer and aphotoinitiator.
 22. The method of claim 14 further comprising embossingthe formed case.
 23. A method of claim 14 wherein the cover stockmaterial is a porous cover stock material.
 24. A casemaking machinecomprising a curing apparatus.
 25. The machine of claim 24 wherein thecuring apparatus is the source of actinic or ionizing radiation or asource of moisture.